In the prior art, it is known to detect leaks in vacuum equipment by detecting how much of a light gas, such as helium, flows into the vacuum equipment from a pressurized source in an ambient atmosphere. The vacuum equipment is connected to a filter that passes the light gas and rejects heavier gases which are in the equipment but are not to be detected. Gas passed through the filter flows to a gas monitoring instrument, such as a mass spectrometer. The vacuum equipment is evacuated to a relatively low vacuum by a mechanical fore or roughing pump while the filter and monitoring instrument are evacuated to a higher vacuum, generally by the combination of the fore pump and a higher vacuum pump, such as a diffusion pump. It is also necessary to vent the vacuum equipment and/or monitoring instrument to the atmosphere from time to time. While the vacuum equipment and monitoring instrument are vented it is desirable to disconnect the pumps from the vacuum equipment and the monitoring instrument, so that the pumps can be maintained in a vacuum state during venting and are not excessively loaded after venting. After venting has been performed, the roughing pump is connected to the vacuum equipment and monitoring instrument to evacuate them to a low vacuum level while the diffusion pump remains in a high vacuum state and no gas is permitted to flow into it. After the vacuum equipment and monitoring instrument have been evacuated to the low vacuum level by the roughing pump, the diffusion pump is connected to the monitoring instrument, to reduce the pressure in it to the high vacuum level. If only the equipment is vented, somewhat the same sequence is followed except that the monitoring instrument remains connected to the diffusion pump at all times, but a flow path between the diffusion pump and both of the roughing pump and vacuum equipment is blocked.
One type of prior art system, as disclosed in Briggs, U.S. Pat. No. 3,690,151, commonly assigned with the present invention, employs a diffusion pump as a filter to pass the light gas to the monitoring instrument to the exclusion of heavier gases, as well as for the usual purpose of evacuating the monitoring instrument. The vacuum equipment being monitored for leaks and the monitoring instrument are respectively connected to a foreline and high vacuum inlet of the diffusion pump. The diffusion pump effectively functions as a filter to enable a significant percentage of the light gas to flow from the vacuum equipment to the monitoring instrument, while virtually preventing the flow of heavy gases, such as water vapor and nitrogen, between the vacuum equipment and monitoring instrument. There is back-diffusion of the light gas through vaporized jets of a diffusion pump fluid, usually an organic oil. The heavy gases, however, cannot back-diffuse through the oil vapor jet as easily. The monitoring instrument is responsive only to the light gas leaking from the vacuum equipment and relatively accurate indications of the amount of light gas leaking from the monitored equipment are obtained. Commercial equipment utilizing this principle has been extensively marketed under the trademark "CONTRAFLOW".
Prior art leak detectors utilizing a filter, as described broadly above, or in connection with the "CONTRAFLOW" type device, have employed several valve assemblies to provide the required isolation between the diffusion pump, roughing pump, vacuum equipment being monitored, filter and/or analyzing instrument. The several valves must be activated in a particular sequence to provide the required isolation during venting of the vacuum equipment and/or the monitoring instrument. The valves must also provide isolation between the diffusion pump and roughing pump as well as the vacuum equipment and monitoring instrument during transitional periods when the equipment and instrument are being evacuated to the roughing pump vacuum and when the instrument is evacuated to the diffusion pump vacuum. The multiple valve assemblies employed in the prior art are relatively expensive and are subject to being operated in an incorrect sequence. If the sequence is not performed correctly, there is a compromise of the vacuum of the roughing and/or diffusion pump. Of course, if the roughing pump and/or diffusion pump vacuum is compromised, a considerable delay occurs before the desired vacuum of these pumps can be reached.
It is, therefore, an object of the present invention to provide a new and improved vacuum equipment leak detector.
Another object of the invention is to provide a new and improved valving structure for vacuum leak detecting equipment.
A further object of the invention is to provide a new and improved vacuum leak detecting apparatus having a relatively simple valving assembly that is low cost, utilizes a minimum of parts and is relatively light weight.
An additional object of the invention is to provide a new and improved vacuum leak detecting apparatus employing a valve assembly having a relatively foolproof operating sequence.
Another object of the invention is to provide a new and improved vacuum leak detecting apparatus employing a valve assembly that substantially prevents compromising the vacuum of pumps for the apparatus during venting operations and transitory periods following the venting operation, while the apparatus is being put back on line.